Ambient Temperature – The temperature of the air surrounding the actuator. Generally stated as a maximum and minimum for proper actuator operation.

Cycle life- The period of time an actuator will cycle without failure

Double Acting – A characteristic of a piston or diaphragm system in which the energizing pressure acts on both faces of the piston (diaphragm) and operates the system in forward and reverse open/close. Also referred to as “Air-to-Air” operation.

Duty Cycle – The percentage of time a device is allowed to operate over a given period of time. Expressed in percent – “time on” divided by” time off” x 100. Pneumatic actuators have a 100% Duty Cycle. Electric actuators are most commonly available with 25% Duty Cycle motors. In order to prevent overheating the motor, for each 1-minute of operation, 3-minutes of non-operation is required. Duty cycles greater than 25% are generally needed only when additional work loads are encountered, such as valve modulation or in actuation of larger butterfly valves.

Electric Actuator – An electromechanical device used to actuate (open, close or modulate) a valve. An electric motor and gear train is used to actuate the valve.

Fail-Closed – Spring return in a pneumatic actuator which closes the valve upon loss of air pressure. Also referred to as “Air-to-Open” or “Spring-to-Close” operation.

Fail-Open – Spring return in a pneumatic actuator which opens the valve upon loss of air pressure. Also referred to as “Air-to-Close” or “Spring-to-Open” operation.

Fail Safe-A characteristic of the system that ensures that the unit will revert to a safe condition upon the loss of power.

Limit Switches -A set of electrical contacts that are activated mechanically at a pre-selected position. Electrical switches which may be applied to either electric or Pneumatic actuators to supply a signal that the valve cycle has been completed. In Electric actuators, the primary limit switches are used to control the open and closed position of the valve

Manual Override-A capability provided to actuators that allows the manual positioning of the actuator. This is typically engaged when the valve cannot be operated automatically by the actuator.

Maximum Line Pressure – The media pressure against which the valve will have to close.

Maximum Service Temperature – Maximum temperature of the media. Service temperature should be considered in selection of the proper thermoplastic valve material for the application.

Media – The material flowing through a valve.

Modulating – Throttling or regulating flow by varying the position between open and closed.

Moment Arm-The linear distance from the center of rotation upon which a force may act to produce torque.

Mounting Bracket– A machined coupling and plate, spool, or length of rectangular tubing designed to adapt an actuator to a valve.

NEMA Rating – A code established for electrical components by the National Electric Manufacturers Association. The most commonly used NEMA ratings for electric actuator and electrical accessory enclosures are NEMA 4 and NEMA 4X.

NEMA 1: General Purposes – for indoor use without unusual service conditions, primarily to protect components from contact.

NEMA 2: Similar to Type 1 with the addition of drip shields or equivalent. Used where condensation may be severe such as in cooling rooms and laundries.

NEMA 3: Weather Resistant – Protects against weather hazards such as rain and sleet in outside areas such a construction sites, tunnels or subways.

NEMA 4: Watertight and Dust tight – for indoor/outdoor use with a protection from windblown dust, rain or hose directed wash down environments.

NEMA 4X: Watertight and Dust tight – same as NEMA 4 with addition of corrosion resistance.

Pilot Valve– A device acting between the source of air pressure and the actuator that directs air flow to the required actuator air inlet ports.

Pneumatic Actuator – An air operated mechanical device used to actuate (open, close or modulate) a valve. The actuator converts air pressure into mechanical force most commonly using either a piston or diaphragm. The mechanical force output can be either rotational, as in actuation of a ball valve, or linear as commonly used in actuation of a diaphragm valve.

Positioner – A control accessory that accepts a varying input signal and directs air to the actuator to position the valve for flow control

Rotary Actuator- A device that provides torque or rotating movement to a rotary valve.

Scotch Yoke-A device that translates linear motion to rotary motion. The linear motion is defined by a pin or roller element trapped within a channel in the rotary element.

Solenoid Valve -An electrically powered device with a movable element that switches flow as a method of controlling actuator position. Double Acting actuators require a 4-way solenoid, Spring-Return actuators require a 3-way solenoid for proper air control. Solenoid valves are available in various NEMA ratings.

Spring Return Actuator– An actuator that contains a spring element having the capability of returning a valve/actuator system to its normal position (open or closed) upon loss of power. Spring returns are most commonly used with pneumatic actuators, but can be used on electric actuators where it is necessary for the valve to open or close by design or by system failure

About Kim O'Neill

Marketing administrator at Assured Automation, a leading provider of automated valves and flow components for industrial process control applications. For over 30 years Assured Automation has provided state of the art automation to a diverse clientele ranging from small equipment manufacturers to Fortune 500 Manufacturing, Chemical and Pharmaceutical companies. The Assured Automation product line consists of a complete offering of standardized automated valve assemblies with a variety of commonly used accessory items. In addition, we offer complete valve automation services where we supply special automated valve assemblies designed around your specified products or your particular applications. Full design capabilities are offered including AutoCAD, Solidworks or other commonly used design and drawing programs. In addition to standard products, Assured Automation develops customized solutions for specific customer challenges. You can find Kim O'Neill on Google+ and LinkedIn.